1. Field of the Invention
The present disclosure relates to an element substrate that adds discharge energy to a liquid and that discharges the liquid and relates to a liquid discharge head provided with the element substrate.
2. Description of the Related Art
A liquid discharge head that discharges a liquid is required to discharge small droplets each having a volume of 2 pl or smaller, for example. By applying such small droplets on a record medium at high density, an image quality with high definition can be obtained. Due to reduction in size of the droplets, the number of discharges dramatically increases. In increasing the number of discharges, a limitation in the number of discharges is encountered when only the ejection frequency is increased and, as the ejection frequency is increased, an adverse effect in that the discharge speed decreases occurs. In order to avoid reduction in the discharge speed and to discharge a predetermined amount of liquid in a shorter time, an element substrate in which a large number of discharge ports are arranged at high density is employed.
Incidentally, in an element substrate that discharges a liquid, a problem has been met in that the viscosity of the liquid becomes high when the temperature of the liquid decreases. In order to avoid such a problem, a technique has been employed in which the liquid is heated before being supplied to an acting chamber that makes discharge energy act on the liquid. However, in an element substrate that discharges small droplets, due to an increase in viscosity that is caused by increase in the temperature of the liquid, a problem of drop in the discharge characteristics is encountered. In other words, the heated liquid accumulated in the acting chamber evaporates through the discharge port. In the element substrate that discharges small droplets, the amount of liquid that is discharged from each discharge port is small and even with a small amount of solvent evaporation, the viscosity of the liquid easily increases. Furthermore, since the discharge ports and the acting chamber are relatively small, they are easily affected by the increase in the flow resistance of the liquid caused by the increase in viscosity. Such problems are prominent in pigment ink that easily agglomerate or highly functional ink with a high additive resin content.
Increase in the flow resistance causes the discharge characteristics of the element substrate to drop. Due to drop in the discharge characteristics, there are cases in which the element substrate fails to discharge the liquid unless a recovery process is performed in the liquid supply channel from the discharge port to the acting chamber.
US Patent Application Publication Number 2009/0160896 discloses an element substrate that is controlled so that a liquid inside an acting chamber is not heated more than needed.
In the element substrate described in US Patent Application Publication Number 2009/0160896, a heat generation element serving as an energy-generating element preliminarily heats the liquid inside the acting chamber to a predetermined temperature and, then, discharges the liquid after the heat generation element has boiled the liquid. However, it is difficult to rapidly heat the liquid with the quantity of heat of the preliminary heating. Accordingly, when under a low-temperature environment, a long standby time is needed until the liquid is heated to the predetermined temperature with the preliminary heating, and the throughput of the element substrate decreases.